Electric vehicles

The REVA electric car was launched in June 2001 in Bangalore and is ex-
ported to the UK as the G-Wiz. The G-Wiz’s electric motor has a peak
power of 13 kW, and can produce a sustained power of 4.8 kW. The motor
provides regenerative braking. It is powered by eight 6-volt lead acid
batteries, which when fully charged give a range of “up to 77 km.” A full
charge consumes 9.7 kWh of electricity. These figures imply a transport
cost of 13 kWh per 100 km.

Manufacturers always quote the best possible performance of their
products. What happens in real life? The real-life performance of a G-Wiz
in London is shown in figure 20.21. Over the course of 19 recharges,
the average transport cost of this G-Wiz is 21 kWh per 100 km – about four
times better than an average fossil fuel car. The best result was 16 kWh
per 100 km, and the worst was 33 kWh per 100 km. If you are interested
in carbon emissions, 21 kWh per 100 km is equivalent to 105 g CO2 per km,
assuming that electricity has a footprint of 500 g CO2 per kWh.

Now, the G-Wiz sits at one end of the performance spectrum. What if
we demand more – more acceleration, more speed, and more range? At
the other end of the spectrum is the Tesla Roadster. The Tesla Roadster
2008 has a range of 220 miles (354 km); its lithium-ion battery pack stores
53 kWh and weighs 450 kg (120 Wh/kg). The vehicle weighs 1220 kg and
its motor’s maximum power is 185 kW. What is the energy-consumption
of this muscle car? Remarkably, it’s better than the G-Wiz: 15 kWh per
100 km. Evidence that a range of 354 km should be enough for most people
most of the time comes from the fact that only 8.3% of commuters travel
more than 30 km to their workplace.

I’ve looked up the performance figures for lots of electric vehicles –
they’re listed in this chapter’s end-notes – and they seem to be consistent
with this summary: electric vehicles can deliver transport at an energy cost
of roughly 15 kWh per 100 km. That’s five times better than our baseline
fossil-car, and significantly better than any hybrid cars. Hurray! To achieve
economical transport, we don’t have to huddle together in public transport
– we can still hurtle around, enjoying all the pleasures and freedoms of solo
travel, thanks to electric vehicles.

Figure 20.20. Electric vehicles. From left to right: the G-Wiz; the rotting corpse of a Sinclair C5; a Citroën Berlingo; and an Elettrica.

Figure 20.21. Electricity required to recharge a G-Wiz versus distance driven. Measurements were made at the socket.